Sampling small older populations:

Methods and challenges of a dementia prevalence study

NZSA2024

Claudia Rivera-Rodriguez, PhD

New Zealand changing population

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The need for a prevalence study

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Feasibility study (2020)

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  • Demonstrated that a prevalence study was feasible in Māori, Chinese, Indian and Pākehā

  • We found that the sampling/doorknocking strategy was reasonable

  • We were able to train up multi-ethnic interviewers

  • Response rate at the door-knocking stage was 75% but at subsequent stages was about 25%

IDEA Study

  • Aim: Establish the true current prevalence of dementia in NZ

  • Population: Chinese, Indian and Pākehā 65yo+

  • This talk presents the sampling design and lessons learned from the IDEA study

  • There is separate study for Māori(running at the moment too)

Sampling strategy

Frame: Territorial autorities

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Sampling phases

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Phase 1

  • Stratified by TA and rurality

  • Oversampling of Chinese/Indian(65+) dense areas

Phase 2

  • A proportion of meshblocks is sampled from each area selected at phase 1

  • Sampling of meshblocks is proportional to the density of Chinese and Indians.

Phase 3

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Sample sizes for each domain

  • We run lots of simulations to identify sensible sample parameters: Image

Sample sizes for each domain

We decided on a margin of error of about 0.03,

Our design: inclusion probabilities-areas

Challenges (So Far)

  • Meshblocks with only businesses, not residential dwellings: We replace these with the closest meshblock (based on selection probability) from the same area.

  • Door-knocking is expensive and difficult.

  • Training of interviewers in 4 different languages

  • Consent rates vary across ethnicities: Sampling weights will need adjustment for this.

  • Data processing from questionnaires in four different languages.

How is the recruitment going?

Thank you!